In the conventional signature scheme used in the E-cornmerce transaction, the validity of a signature value is determined at the point of signature generation and never changes. Signers cannot generate the so-called ‘future signature’ which is not currently valid but becomes valid from a future time t.
A naive way to achieve this is signing with a statement such as “the signature of message m becomes valid from the future time t.” This, however, has several drawbacks. First, and least serious, the verifier is required to be aware of the current time. When time is generalized to arbitrary events (i.e., ‘the signature of message m becomes valid if the event e happens’), this becomes even more problematic. More seriously, however, in the naive solution the signer loses control over the validity of the future signature, i.e. even the real signer cannot make the signature valid before the time t. This means the signer has to wait until time t. It could be undesirable in certain situations. For example, in the case of debt repayment, after a borrower signed a check to indicate the repayment day (e.g. due day), he may have the desire to repay his debt earlier to improve his credit history.
Alternatively, the signer can issue a new, independent signature of message m before time t. This solution, however, can also be undesirable in certain situations. For example, in case the message m carries some monetary value, the first end needs to make sure that no “double spending” occurs (i.e., to somehow revoke the original signature, so that it does not become valid at time t).
Therefore, it is necessary to figure out a solution where the signer can issue a future signature so that at least the following properties are satisfied:    (1) At the time of creation, the verifier is sure that the signature will become valid by time t, even if the signer refuses to cooperate after she produces the future signature.    (2) The legal signer can make the future signature valid at any time after the initial creation.
To realize these properties in E-Commerce platforms, a new primitive, which has a great promise to be a very useful tool, is called Time Capsule Signature.
A time capsule signature involves a first end (such as a signer), a second end (such as a verifier) and a time server. The first end can issue a future signature indicated by a committed time t, and enjoys the following properties: first, the second end can verify immediately that the signature will become valid at time t; secondly, the signature will automatically become valid at the committed time t, even without the cooperation of the first end; and moreover, the first end has a privilege to make the signature valid before time t. The action of validating the signature before the time t is known as pre-hatch, as opposed to hatch the signature at time t when some additional information is published by the time server.
Moreover, in some scenarios, it is needful to distinguish a pre-hatched signature from a hatched signature. In the above debt repayment case, a pre-hatched signature has to be identified when a signer intentionally pre-hatches the signature for increasing his credit history. On the other hand, under the property of indistinguishability of the conventional signature scheme, the time server has to be fully trusted, otherwise, there is no way to tell if a signature which becomes valid before time t is generated by the actual signer or a cheating time server.
It is therefore desirable to have systems and methods for advancing the committed time t based on the willing of the first end. Meanwhile, the systems and methods can distinguish a pre-hatched signature from a hatched signature.